1. Field of the Invention:
The invention relates to an actuator for a rotary valve, or similar mechanism.
2. Description of the Prior Art:
Actuators for rotary valves usually use a crank arm mechanism, scotch yoke, chain drive, rack and pinion, or vane type operator in order to rotate the valve through 90.degree., 180.degree. or any desired degree of turning. Although these devices achieve the desired results, they generally are large, in some cases overhang the valve flanges, and in general have a high side thrust component. It is desirable to produce an actuator for a rotary valve or the like, which is compact, simple in construction and operation, efficient and trouble-free.
It is acknowledged that ball screw mechanisms are old in the art, and reference is made to the following U.S. patents as being of interest in this connection, all of which have a rotary input to generate a linear output:
______________________________________ 476,304 June 7, 1892 Gratt 611,832 Oct. 4, 1898 Coughlan 3,758,938 Sept. 18, 1973 Simmons, et al 4,149,430 April 17, 1979 Geppert ______________________________________
U.S. Pat. No. 4,114,470, entitled "Relating To Pressure Fluid Operated Actuators", issued Sept. 19, 1978, discloses a rotary actuator incorporating an enclosure with a rectilineal slideway along which a slide member is movable which has means at one end of the slide member for moving the member along the slideway and means at the other end of the slide member for restraining the slide member from rotary movement. The slide member carries a screw threaded nut assembly which engages a worm screw forming a part of an output shaft which is rotated when the slide member slides. In such an apparatus, conventional pre-loaded acme threads are utilized in a linearly driven, rotatably reciprocable apparatus in which no means are provided for stroke regulation.